WASHINGTON (CNN) – Law enforcement sources confirmed to CNN that so-called "do not destroy" letters have been sent to the State and Defense Departments as part of the ongoing probe into who leaked the name of an CIA officer to a newspaper columnist.

The letters, like previous ones to the White House and CIA, ask recipients not to destroy phones logs, e-mails and other relevant documents.

A government source familiar with the investigation told CNN that by Friday Justice Department investigators will send the White House a letter requesting all documents collected during a recent review of files. The source said it was a routine request in the early stages of gathering potential evidence.

The Justice Department is trying to determine who told syndicated columnist and CNN contributor Robert Novak the name of CIA operative Valerie Plame.

Plame is the wife of former Ambassador Joseph Wilson, who wrote in a New York Times op-ed piece that the Bush administration overstated the threat posed by Iraq during the months before the U.S.-led invasion in March. Wilson claims someone in the White House leaked his wife's name to discredit him and intimidate other critics.

Last week, Wilson suggested that senior White House adviser Karl Rove may have been involved in the leak of his wife's identity. Novak said the name came from two administration officials.

Rove's ties to Attorney General John Ashcroft have led some lawmakers, including one senior Republican, to say he should consider recusing himself from the investigation. Rove was a political adviser during Ashcroft's gubernatorial and Senate campaigns in Missouri.

Specter noted that the investigation is not directly controlled by Ashcroft, but by career prosecutors reporting to FBI Director Robert Mueller. Mueller's 10-year tenure insulates him from White House pressure.

Calls for Ashcroft to recuse himself also came from Democratic Sen. Charles Schumer of New York. Other Democrats have urged that Ashcroft name a special prosecutor to handle the case.

Schumer's press secretary said Justice Department rules hold that a federal prosecutor cannot issue subpoenas of news media phone records without the express written consent of the attorney general. Since media phone records may end up being subpoenaed, Schumer believes Ashcroft should step aside.

But at a Republican news conference, Senate Majority leader Bill Frist said he thinks the Justice Department can handle the investigation. Calls for a special prosecutor or for Ashcroft's recusal "have a partisan flavor to them," he said.

Justice Department spokesman Mark Corallo said the department is keeping its options open.

Meanwhile, the Republican chairman of the House Government Reform Committee met with Wilson and other lawmakers Thursday to determine if hearings on the matter were necessary.

Rep. Tom Davis, R-Virginia "thinks it's pretty clear that information was leaked that shouldn't have been leaked," committee spokesman David Marin said. "What's not clear yet is whether a crime was committed."

The "immediate aim" of the lawmakers is to monitor the Justice Department investigation and make sure it's thorough and objective and to keep an eye on how the White House handles the situation," Marin said

White House spokesman Scott McClellan said Thursday no White House officials have been subpoenaed in the investigation. He said FBI agents have not interviewed any members of the White House staff, but cautioned that he would not necessarily know if White House staffers were being interviewed individually.

Law enforcement sources said interviews with White House officials were most likely to occur in the next few days.

-- CNN Correspondents John King and Kelli Arena and Producers Terry Frieden, Steve Turnham and Ted Barrett contributed to this report.